Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$180.59	4.836%	$189.3233	$189.32	$189.30	$189.30
Purchase #2	$106.38	3.187%	$109.7703	$109.77	$109.75	$109.80
Purchase #3	$135.51	4.492%	$141.5971	$141.60	$141.60	$141.60
Purchase #4	$39.52	4.842%	$41.4336	$41.43	$41.45	$41.40
Purchase #5	$74.43	12.743%	$83.9146	$83.91	$83.90	$83.90
Purchase #6	$184.96	3.151%	$190.7881	$190.79	$190.80	$190.80
Purchase #7	$54.27	9.670%	$59.5179	$59.52	$59.50	$59.50
7 purchase totals =	$775.66		$816.3449	$816.34	$816.30	$816.30